Authors:

Frank Bridges(UC Santa Cruz)

Geza Kurczveil(UC Santa Cruz)

Lisa Downward(UC Santa Cruz)

John J. Neumeier(Montana State University)

Recently we have proposed a complex 2-site polaron model (which
we call a dimeron) that exists for temperatures near and above
the ferromagnetic transition temperature, T$_c$ [1]. The dimeron
has a hole delocalized over two Mn sites (i.e. a hole and an
electron share the two Mn sites) and the two Mn sites have a
reduced distortion compared to the remaining Jahn-Teller
distorted electron sites. Magnetic clusters just above T$_c$ are
likely clusters of these dimeron quasiparticles. The average
valance of the two Mn sites in the dimeron is 3.5 and the spin is
7/2. We show that the Mn K-absorption edge is much better
described as a sum of a 3.5 valence edge (fraction 2x) plus a 3
valance edge (fraction 1-2x), compared to earlier simulations
using x CaMnO$_3$ plus 1-x LaMnO$_3$. We also show that fitting
the Mn-O peak to a sum of two experimental Mn-O standards leads
to a similar result as in the earlier study - a fraction 2x of
lower distorted Mn sites (dimerons) and a fraction 1-2x of
more distorted sites with 1 e$_g$ electron. Both support the
proposed complex - 2-site polaron model.\newline
Supported under NSF grant DMR0301971.\newline
[1] L. Downward et. al., Phys Rev Lett 95, 106401 (2005).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.MAR.U13.2